Van der Waals Epitaxial Growth for High Performance Organic-Free Perovskite Solar Cell: Experimental and Theoretical Insights

All-inorganic perovskite solar cells (PSCs) are most promising in yielding stabilized power conversion efficiencies (PCE) as compared to their hybrid organic–inorganic counterparts. However, all-inorganic PSCs have suffered from low efficiency due to significant charge carrier recombination within perovskite active layer (PAL) bulk and at the carrier selective interfaces (CSI). Boosting the PCE through the remedy to both issues seems to be the only Achilles-Heal on their way to commercialization. Here, a synergistic approach of liquid-exfoliated molybdenum disulfide (MoS₂) at the PAL (CsPbIBr₂)/hole transport layer (NiO) interface to enhance the perovskite grain growth and stabilize the hole transport layer (HTL)/PAL interface against the carrier recombination within the PAL bulk and at the interface is reported. The in-plane coupling between MoS₂ crystal lattice and CsPbIBr₂ is strongly revealed through transmission electron microscopy (TEM) results, which favored the van der Waals epitaxial growth of CsPbIBr₂ PAL toward the larger crystalline grain sizes, preferential growth along (110), i.e., normal to MoS₂, and low trap-density. Therefore, the PCE of organic-free CsPbIBr₂ PSC is increased to as high as 10.98% under 1-sun illumination, which is 48% higher than the pristine device (7.38%), which concludes that this strategy can be integrated to other analogous perovskite compositions.